In an engine system which utilizes a direct injection fuel delivery system, accurate fuel metering is imperative for efficient operation of the engine system. Fuel control strategies may take into account various delays relating to operation of fuel injectors in the direct injection fuel system in order to maintain accurate fuel control and, more particularly, accurate fuel injection timing. In particular, a control system may send fuel injection signals to one or more fuel injectors with timing that may be advanced in order to account for various types of delays associated with fuel injector hardware so that fuel injection may be performed at a desired time.
For example, some fuel control strategies may advance signal timing to account for opening and closing delays of the fuel injectors. In one example, a fuel injection signal time may be advanced uniformly to account for either an opening delay or a closing delay of a fuel injector needle. In other words, some fuel control strategies may assign a single value to an opening delay and/or a closing delay that may be used for all operating conditions.
However, the inventors herein have recognized that opening and closing delays of a fuel injector may vary according to changes in operating conditions and modes of engine operation. Thus, if constant response time delays are utilized throughout varying operating conditions, fuel metering may become inaccurate. In particular, the commanded fuel injection time may not match the desired fuel injection time due to variance of the actual response time delay compared with the constant response time delay value used by the fuel control system, which in turn, may result in an imbalance of delivered fuel and injection timing among each of the cylinders. The cylinder imbalance may lead to torque variations among the cylinder which may result in increased noise, vibration, and harshness (NVH). Further, the inaccurate fuel metering may lead to some, if not all, cylinders operating rich resulting in reduced fuel economy and increased tailpipe emissions.
Additionally, the inventors have also recognized that during modes of engine operation where multiple injection events occur during a cylinder event (e.g. split injection), changes in fuel pressure as well as duration between fuel injections may affect the response time delays associated with the fuel injector. In particular, after the end of injection of a fuel injection event, there exists a transient condition where fuel injector needle bounce occurs and the needle bounce may affect the response time delays of the fuel injector since the fuel injector needle may have to travel less distance at the start of injection. Furthermore, changes in fuel pressure may affect fuel injector needle bounce and the response time delays of the fuel injector.
In one approach, at least some of the above issues may be addressed by a method for controlling fuel injection timing of at least one fuel injector in a direct injection fuel delivery system of an internal combustion engine during a mode of engine operation where a plurality of fuel injection events are performed by the at least one fuel injector during a cylinder event is provide. The method includes, during a first fuel injector needle bounce condition following the end of injection of a first fuel injection event, sending a start of injection signal for a second fuel injection event at a first time, and during a second fuel injector needle bounce condition following the end of injection of the first fuel injection that differs from the first fuel injector needle bounce condition, sending the start of injection signal for the second fuel injection event at a second time that is earlier than the first time.
By recognizing transient conditions where needle bounce occurs and actively compensating for the transient conditions by modifying the opening delay time of the fuel injector needle based on fuel pressure and fuel injector needle bounce behavior, fuel injection timing accuracy may be maintained even as operating conditions change. In this way, fuel metering accuracy may be improved across the operating range of the engine system and cylinder balancing and fuel economy performance may be improved and tailpipe emissions may be reduced.
Furthermore, the improved accuracy of fuel injection timing generated from the control routine may provide greater control resolution which in turn may facilitate the use of fuel injector hardware with looser operational tolerances without a substantially reduction in fuel metering accuracy. In this way, cost of components may be reduced while still maintaining accurate fuel metering.